For using polysiloxanes in polar media, it is necessary to incorporate polar groups in the siloxane. For this purpose, numerous possibilities are described in the literature.
The synthesis of siloxane-carbonate block copolymers is known from the patent literature (for example, from U.S. Pat. No. 3,189,662; U.S. Pat. No. 3,821,325 or U.S. Pat. 4,657,989). In the majority of cases, it is a question of polydimethyl-siloxanes, which are terminated with bisphenol A and obtained by the reaction of the reactive end group of polysiloxanes with bisphenols in the present of phosgene or diaryl carbonates. Linkage is accomplished in these reactions predominantly over the hydrolyrically unstable Si--O--C bonds.
Siloxanes with SiC-linked carbonate groups are described by Boileau et al. in Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem., 1990, 31 (2), pages 420-1). The synthesis is accomplished by a hydrosilylation reaction of SiH siloxanes with allylphenol carbonate. However, according to information from the authors, the reaction is quite complex and does not proceed satisfactorily in the desired reaction, because about 50% of the carbonate functions are decomposed under the reaction conditions, carbon dioxide being split off and SiOC-functionai siloxanes being formed.
In Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem., 1994, 35 (1), pages 496-7), Zhu et al. described the transesterification of allyl-functionai 1,2 diols, such as 5-hexene-1,2-diol with diethyl carbonate and the subsequent, platinum-catalyzed hydrosilylation reaction of the product with SiH siloxanes in different solvents, such as acetone or acetonitrile. According to the authors, the side reactions are largely but not completely avoided by this step of the method. Furthermore, it is a disadvantage of this method that the reaction is carried out at moderate temperatures (60.degree. C.) and therefore requires quite a long time. Moreover, the addition of solvent not only decreases the volume yield of the method, but also makes it necessary to distill off the solvent in an additional step of the method, which is associated with costs.
It has now been found that organopolysiloxanes, which contain cyclic carbonate groups, can be synthesized easily by a simple method.